Chapter 6. Files
For obvious reasons, the browser has historically had very limited ability to access the filesystem. HTML forms have been able to upload files, and certain HTTP headers make it possible for a user to download files from the server. But outside of those specific features, the browser has not been able to access files on the local filesystem. In general this is a good thing. I don’t want every web page I visit to be able to look around my hard drive!
This does not create any new security problems, because the application already had access to this data by uploading it to the server, then downloading it again into the browser.
As of this writing, these features are supported in Firefox, Chrome, and Opera. For Safari and Internet Explorer, the Flash plug-in will work to allow file drag-and-drop.